kVA Calculator

The kVA Calculator converts between kVA (apparent power), kW (real power), amps (current) and volts (voltage) for DC, single-phase and three-phase systems. Enter any two known values and it instantly returns the full picture — apparent power, real power, reactive power (kVAR), current and voltage — shown on an animated, to-scale power triangle, along with generator and UPS sizing suggestions.

What is kVA?

kVA stands for kilovolt-amperes and measures apparent power — the total power flowing in a circuit, the product of voltage and current. It is the figure used to rate transformers, generators and UPS units because those devices must handle the full current regardless of how much of it does useful work.

kVA vs kW vs kVAR

• kVA (apparent power) — the total power supplied, volts × amps. This is what the wiring, transformer and generator must carry.
• kW (real power) — the portion that does actual work, such as turning a motor or producing heat. kW = kVA × power factor.
• kVAR (reactive power) — power that shuttles back and forth to build magnetic fields in motors and transformers but does no net work. kVAR = √(kVA² − kW²).

These three form the power triangle: kW is the horizontal side, kVAR the vertical side, and kVA the hypotenuse. The angle between kW and kVA is the phase angle φ, where the power factor equals cos φ.

kVA Formulas

How to Convert kVA to Amps

Rearranging the formulas above for current gives:

kVA to Amps Reference (Three-phase, 400 V)

Typical full-load current for common three-phase kVA ratings at 400 V line-to-line:

What is Power Factor?

Power factor is the ratio of real power to apparent power (kW ÷ kVA), a number from 0 to 1. It describes how effectively current is turned into useful work. Purely resistive loads such as heaters and incandescent lamps have a power factor near 1, so their kVA and kW are almost equal. Inductive loads such as motors, transformers and fluorescent ballasts typically run at 0.7–0.9, meaning they draw more kVA than the kW they deliver.

How to Size a Generator or UPS in kVA

Because generators and UPS units are rated in kVA (or VA), you size them against the apparent power of the load, not just the kW. A common approach:

• Add up the running load in kVA across everything that will run at the same time.
• Add headroom — roughly 25% is a typical margin for surges and future growth. This tool suggests a continuous generator rating on that basis.
• Account for motor starting — motors can draw 3–6× their running current for a moment on start-up, so motor-heavy loads need extra margin.
• UPS units are rated in VA; match the VA rating to your kVA load with about 20% headroom and check the battery runtime you need.

These are rules of thumb for a first estimate. Always confirm the final rating with the equipment nameplate data and a qualified electrician.

How to Use This Calculator

1. Choose what to solve for: current (amps), voltage (volts), or power (kVA/kW).
2. Select the system: DC, single-phase AC or three-phase AC, and enter the power factor for AC systems.
3. Enter the two known values, for example kVA and voltage, or voltage and current.
4. Review the results: the full kVA, kW, kVAR, volts and amps breakdown, the animated power triangle, the power-factor utilization bar, and generator / UPS sizing suggestions.

Frequently Asked Questions

What is the difference between kVA and kW?

kVA is apparent power, the total power supplied to a circuit. kW is real power, the portion that does useful work. They are linked by the power factor: kW = kVA × power factor. In a perfect resistive load the power factor is 1, so kVA and kW are equal; with reactive loads such as motors the power factor is below 1 and kVA is larger than kW.

How do you convert kVA to amps?

For a single-phase system, amps = kVA × 1000 ÷ volts. For a three-phase system, amps = kVA × 1000 ÷ (1.732 × volts), where volts is the line-to-line voltage. For example, 10 kVA at 240 V single-phase draws about 41.7 amps.

How do you convert kVA to kW?

Multiply kVA by the power factor: kW = kVA × power factor. For example, 25 kVA at a power factor of 0.8 equals 20 kW. To go the other way, divide kW by the power factor: kVA = kW ÷ power factor.

What is power factor?

Power factor is the ratio of real power (kW) to apparent power (kVA), a number between 0 and 1. It measures how effectively current is converted into useful work. Resistive loads such as heaters have a power factor near 1, while inductive loads such as motors and transformers typically run at 0.7 to 0.9.

How do I size a generator in kVA?

Add up the running load in kVA and add headroom for surges and future growth, commonly about 25 percent. Motors can draw several times their running current when starting, so motor-heavy loads need a larger margin. This calculator suggests a continuous generator rating with 25 percent headroom as a starting point.

Is kVA bigger than kW?

kVA is always equal to or greater than kW. Because kW = kVA × power factor and the power factor is at most 1, kW can never exceed kVA. The two are equal only when the power factor is exactly 1, as in a purely resistive or DC circuit.

Additional Resources

• AC Power (apparent, real, reactive) - Wikipedia
• Power Factor - Wikipedia